In marine mammals’ battle of the sexes, vaginal folds can make the difference

Patricia Brennan has made a splash with her studies of genitalia and fit

FERTILE FOLDS In harbor porpoises (one shown), females have vaginal folds (3-D endocast shown below) that may help them exert control over fertilization.

Solvin Zankl/Alamy Stock Photo

The battle of the sexes, at least among certain ocean mammals, may come down to well-placed skin folds, suggests research by Patricia Brennan, an evolutionary biologist at Mount Holyoke College in South Hadley, Mass., and colleagues.

In some species, enhanced male-female genital fit has evolved over time in ways that make mating easier. This is an example of what scientists call congruent evolution. In other species, genital anatomy reflects a battle, as shape and form change over time to give one sex an edge in control of fertilization. Fittingly, this is called antagonistic evolution.

Brennan’s recent collaboration, examining genitalia of porpoises, dolphins and seals, required extra creativity. In previous studies, her team used saline to inflate preserved penises from birds, snakes, sharks and bats. But the tough, fibroelastic penises of the cetaceans would not inflate with saline alone. So her collaborator, Diane Kelly, a penis biomechanics expert at the

This article is only available to Science News subscribers. Already a subscriber? Log in now. Or subscribe today for full access.